Low Compression bent rod? WPS

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Sharpy
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Low Compression bent rod? WPS

Post by Sharpy » Wed Jun 12, 2019 7:42 pm

Having recently purchased a WPS500 I like to use it where possible even when I have a fair idea whats wrong to aid learning whats good and bad for when I have no idea. So I thought I'd share what I'd taken in case it may help others and also if I may be missing something which is highly likely being I'm green to both the Wps and the scope.
So the vehicle is a 2013 MAN HGV 32 tonne rigid with a 10.5 litre 6 cylinder 360hp Biturbo Diesel Euro 5, I pretty much diagnosed the lorry over the phone as having bent con rod as the complaint was it got parked Friday afternoon with no issues then Monday morning it had a flat battery :lol: . They eventually got it going but now it sounds terrible and is smoking badly and the fumes smell of diesel. The vehicle got recovered to us and I didn't change my mind on the diagnosis after hearing it run. I realised that although it was likely that the engine is going to be stripped I needed to confirm what I thought and try and identify which cylinder was responsible I also needed to figure what was responsible for causing it to hydro-lock in the first place as it may not be obvious once the engine is apart.
The first thing was scan it for faults and although I don't have the codes right now it seemed to be pointing to cylinder 5 as having a fuel related issue, I will update this later. Also a visual inspection revealed the oil level to be high although not excessively with no signs of dilution or contamination and the coolant level low but it turns out that coolant loss has been regarded as normal recently with no signs of an external leak. Next I decided to do a relative compression test with the cam sensor as a sync so I could have the ignition turned off so it didn't start.
As to note this is a single (hollow) cam 24v with manually adjustable rockers.
Attachments
MAN_TGS_2013_Diesel_RELATIVE.psdata
(7.18 MiB) Downloaded 30 times
Last edited by Sharpy on Wed Jun 12, 2019 9:46 pm, edited 1 time in total.

Sharpy
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Re: Low Compression bent rod? WPS

Post by Sharpy » Wed Jun 12, 2019 7:58 pm

The next step was to run the engine to show the Cam signal against an injector current to ID the offending cylinder, I used cylinder 2 as it was the easiest to get an amp clamp round at the ecu because the injectors are fitted under the rocker cover which is a mission to get off due to the air cleaner being mounted over the top of the engine. I also decided as I had 4 channels I should use them so I used the Wps to capture the exhaust pulses in the tailpipe and the other channel to monitor the fuel rail pressure in case the hydro-lock was caused by an injector being stuck open flooding the cylinder.

I also used the overlay app to add the 4 stroke cycle to the exhaust pulse capture to further confirm that it is cylinder 6 with the issue and it shows that whilst cylinder 4 is injecting cylinder 6 is on its exhaust event, at this point I should add that the firing order on this engine is 153624.
Attachments
overlayrx63hkw.png
MAN_TGS_2013_Diesel_IDLINGWPSCYLID.psdata
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Sharpy
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Re: Low Compression bent rod? WPS

Post by Sharpy » Wed Jun 12, 2019 8:30 pm

Due to the even pulses in the fuel rail pressure I was happy enough the injectors weren't the cause of the hydro-lock added to it being the rear most cylinder and with the engine angled slightly backwards points me to something entering via the intake.
Normally I would suspect the Egr cooler dumping coolant into the intake as they are a known weakness on these but this one had an issue a little over a year ago with coolant loss and coolant found in the intake so the Egr & Cooler was bypassed as a 7 day measure to verify the need off a 5k part, it did resolve the problem but it got forgot about and before you know a year has gone by with no issue, there is also high and low pressure water cooled inter coolers that could be the source if it is a coolant related failure plus the usual head/gasket/liner possibilities.
I took captures of the intake and crankcase pulses with the Wps but I'm unable to pick out anything in those although I wasn't expecting a vacuum in the crankcase?
Attachments
MAN_TGS_2013_Diesel_INTAKE.psdata
(13.04 MiB) Downloaded 22 times
MAN_TGS_2013_Diesel_CRANKCASEPRESSURE.psdata
(4.7 MiB) Downloaded 27 times

Sharpy
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Re: Low Compression bent rod? WPS

Post by Sharpy » Wed Jun 12, 2019 9:02 pm

I decided at this point I needed to access and remove injector 6 and upon removing the rocker cover a visual inspection of the cam/valve gear revealed nothing and there was still no signs of oil contamination. After confirming the compression was low with a manual gauge I done an in cylinder with the Wps, as I had the channels I left the relative and cam sync in place.
MAN_TGS_2013_Diesel_WPSINCYLINDER6.psdata
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I then removed no.5 and done the same tests as a comparison


MAN_TGS_2013_DieselWPSINCYL5GOOD.psdata
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I realise that I should have blocked the intake for more definition but that's not a simple task but I will redo them when the time comes to strip it.

I used the rulers and measurements with scaling to check the timing of exhaust valve opening and I think there might be a 5 degree difference between the 2 cylinders and although there is a possibility it could have spun a cam lobe due to the hollow cam fitted to these but I was thinking that if it has a bent rod then that will affect the duration the piston is below its normal lowest point but I would like others opinion on that as I do tend to try and make the facts fit the theory.

My next step is probably to remove the sump an pressurize the cooling system so I can check the rod and also check for coolant leaks as the charge pipework passes through the sump also :|

Well I hope I haven't bored you with my day and if anyone has any input it would be appreciated.

Steve Smith
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Re: Low Compression bent rod? WPS

Post by Steve Smith » Thu Jun 13, 2019 12:00 pm

Hello Sharpy, first of all thank you so much and you are far from boring us with such valid detail

I think you have this sewn up for sure but in an attempt to provide more evidence of piston duration below its lowest point I have used the Reference Waveform Feature to align cylinders 5 & 6 to compare the expansion pocket pressure and pressure rise time (compression event)
This can be challenging due to piston/crankshaft speed variations given the varying "pressure loading" from the good and bad cylinder compressions.

Either way, with that said we have "near alignment" below and we can see a difference in the Expansion Pocket pressure towards BDC on the Expansion stroke at approx. 151 degrees ATDC (-119.5 mbar bad cylinder - 291.3 mbar good cylinder)
SHARPY.png
Cyl 5 & 6
Assuming our valves and piston rings to be sealing effectively (on cylinders 5 & 6) then the difference in the depth of the expansion pocket is due to variations in effective piston stroke. (With a deformed Con Rod the compression ratio is now lower)

It's a tough call to gauge the difference between exhaust valve openings (Cyl 5 &6) without increasing the expansion pocket (blocking intake) given the bad cylinder is not far below atmospheric.

I hear what you are saying about blocking the intake given the turmoil involved during the initial diagnostic stage. (Accessibility and probability come into play here)

The final measurement point looks at the difference in pressure rise time between cylinders.
Using the Rise Time measurement "between the rulers" highlights how the good cylinder pressure increases at a rapid rate in comparison to cylinder 6.

Once again, assuming the valves and rings to be OK, effective piston stroke would present these symptoms

Thank you again Sharpy, take care.....Steve

Sharpy
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Re: Low Compression bent rod? WPS

Post by Sharpy » Thu Jun 13, 2019 7:33 pm

Hi Steve, thanks for taking the time to put that together, I did try a similar thing last night but with nowhere near the detail of yours and they were both the same colour which didn't help but I guess that comes with practice.

I got the chance to question the driver myself today and it turns out over the last 3 weeks he has been putting 2 gallons of water in it a day over 2 stops, funny how I only get this info now.

After carrying out a pressure test on the cooling system to try and find what caused the issue in the first place work has been stopped to save unnecessary labour costs, basically the system held full pressure for 10 hours and I removed the charge pipework from the sump and found it to be bone dry meaning its likely to be linked directly to that cylinder opening up as things expand and because there is a chance it could be the head thats around 6k the customer doesnt want put more labour into stripping the engine when even just a rod,piston & liner was already more than he wanted to spend plus the potential that the injector has been damaged by the compressed coolant the costs could easily hit 10k and the truck is 6 months to old to meet the new ulez standard for London.

If I get a spare 5 mins tomorrow I will try and redo the in cylinder captures for curiosity as I can now block the intake at the sump although the amount of pipework may still cause an issue.

Sharpy
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Re: Low Compression bent rod? WPS

Post by Sharpy » Mon Jun 17, 2019 9:31 pm

Well it seems we may still get an answer on this as I have been asked to continue to try and find the cause first so I am gonna get it running again and warm it up which will give me the chance to give it a thorough wash and hopefully see if anything leaks under pressure when its hot and then I will be stripping it either way, the used engine is a no go the only one has 650000 km and is £4.5k, watch this space...

Sharpy
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Re: Low Compression bent rod? WPS

Post by Sharpy » Sat Jun 29, 2019 11:16 pm

Well this didn’t go quite to plan although we can confirm that it was definitely no.6 and it was most definitely a problem with the rod the only trouble is it’s now on the outside of the engine and we haven’t started stripping it yet :shock:
The customer kept changing his mind as to what was going to happen with it and asked us to reassemble it enough to get it running which we did we then drove it out of the workshop and parked it in the yard whilst we got on with other jobs and he made up his mind.
He then decided it was going to be fixed and asked us to get it back in and start stripping it to see what the damage was and when we went to move it inside no.6 let go punching a hole in the block knocking the compressor clean off
E02ABA50-7068-4A4A-803A-C5AD914092B6.jpeg
and smashed the sump off which made a bit of a mess on the floor
273EC088-1272-4028-BB4F-9F0F4D68D741.jpeg
:roll: needless to say there is no more indecision :D

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